| Feature | Legacy IOS (12.4) | Updated IOS (15.9 or 17.x) | | --- | --- | --- | | | Basic | Fully supported | | EtherChannel | Limited | Full LACP/PagP | | RESTCONF/NETCONF | No | Yes (for SD-Access labs) | | GNS3 Performance | Slow (often 100% CPU) | Optimized (uses VMWare/KVM) |

Finding the right Cisco IOS images for GNS3 in 2026 can feel like a maze, especially with Cisco’s shifting focus toward their own virtualization platforms. While the "golden age" of downloading old